Galling wear of sheet metal stamping tooling is an expensive
issue for sheet metal forming industries. Forming of high
strength steels, particularly in the automotive industry, has led
to accelerated tool wear rates. These wear rates lead to product
quality and die maintenance issues, making galling wear an
expensive issue for automotive manufacturers and the sheet metal
forming industries in general.
Process monitoring allows for the continuous monitoring of
tooling condition so that wear development can be detected. The
aim of this investigation was to develop an in-depth
understanding of the relationship between punch force variation
and wear for implementation in future process monitoring
regimes.
To achieve this aim, the effect of wear and other friction
influencing factors on punch force signatures were investigated.
This required the development of an accurate method for
quantifying galling wear severity so that the relationship
between galling wear progression and punch force signature
variation could be quantified. Finally, the specific effects of
wear and friction conditions on the punch force signatures were
examined.
An initial investigation using a statistical pattern recognition
technique was conducted on stamping force data to determine if
the presence of galling wear on press tooling effected punch
force variation. Galling wear on tooling, changes in lubrication
type, and changes in blank holder pressure were all found to
effect variation in punch force signatures shape. A new galling
wear severity measurement methodology was developed based on
wavelet analysis of 2D surface roughness profiles that accurately
provided an indication of the location and severity of galling
wear damage. Using the new method for quantifying galling wear
severity in the relationship between punch force variation and
galling wear progression was investigated, and a strong linear
relationship was found. Finally, two prominent
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forms of punch force signature shape variation were linked to
friction conditions driven by wear, lubrication, and blank holder
pressure.
This work describes and quantifies the relationship between
galling wear and punch force signature variation. A new
methodology for accurate measurement of galling wear severity is
presented. Finally, specific forms of punch force signature
variation are linked to different friction conditions. These
results are critical for future implementation of punch force
based galling wear process monitoring and a significant reduction
in costs for the metal forming industries
